Molecular Mechanisms of Sex Determination and Differentiation

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This international collaborative research is to combine a variety of approaches and animal systems to the study of sex determination and sexual differentiation. Sex change in the endemic, Hawaiian wrasse Thalassoma duperrey provides an ideal model system to investigate mechanisms of sex determination and sexual differentiation. We first used immunocytochemical methods to detect gonadal sites of P450 cholesterol side-chain cleavage enzyme (P450scc) in the wrasse at different stages of in the sex change process. P450scc cells were predominantly in the theca layr of normal females. As females underwent sex change, P450scc localization shifted from the theca layr to the interstitium. P450scc cells appeared to increase in number midway through sex change. The gonad's ability to produce estrogens, however, is permanently lost in the earliest stages of sex change. The levels of aromatase mRNA and protein, the enzyme responsible for converting androgens to estrogens, was undetectable in testes … More and transitional gonads. In contrast, protein levels of 11beta-hydroxylase, the enzyme responsible for 11-ketotestosterone production increase towards the end of sex change process.In this collaborative research, we also examined immunocytochemically the initial differentiation and development of steroid-producing cells during gonadal sex differentiation in tilapia Oreochromis niloticus using polyclonal antibodies against four steroid-metabolizing enzymes (P450scc, 3beta-HSD,P450c17, P450arom). Immunoreaction for P450scc, 3beta-HSD,P450c17, and P450arom became evident for the first time in gonads of genetically females examined at several days before morphological sex differentiation. In contrast, positive immunostaining for all four steroidogenic enzymes was not easily identified in the testes during sex differentiation. A weak staining for P450scc, 3beta-HSD and P450c17, but not P450arom, was present in the tissue surrounding the efferent duct in testes 30 days after hatching. The number of immunoreactive cells as well as the intensity of staining ware increased in testes just before the onset of spermatogenesis. Taken together, these findings suggest that estrogens play an important role in ovarian differentiation in fish. The results of this collaborative research also suggest an important role of estrogens in temperature-dependent sexual differentiation in reptiles. Less